<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script type="text/javascript">
        function disp_alert() {
            alert("我是警告框！！")
        }
    </script>
</head>
<body>
<input type="button" onclick="disp_alert()" value="显示警告框"/>
</body>
</html>